Carbon nanotube adducts and methods of making the same

ABSTRACT

The invention provides an adduct comprising a carbon nanotube and a transitional metal coordination complex, wherein the metal of the complex is attached by a covalent linkage to at least one oxygen moiety on the nanotube.

This invention was made with Government support under Grant No. 22245 bythe Petroleum Research Fund, and Grant No. 24027 by Sigma Xi.

BACKGROUND OF THE INVENTION

The present invention relates to the art of nanotechnology, and inparticular, to carbon nanotube technology, its function and structure.

A carbon nanotube is a single graphene sheet in the form of a seamlesscylinder. The ends of a nanotube typically have hemispherical caps. Thetypical diameter of a nanotube ranges from about 1 nm to 10 nm. Thelength of a nanotube potentially can be millions of times greater thanits diameter.

Since their discovery in the early 1990s, carbon nanotubes have been thefocus of intense study due to their very desirable and uniquecombination of physical properties. They are chemically inert, thermallystable, highly strong, lightweight, flexible and electricallyconductive. In fact, carbon nanotubes may potentially be stiffer andstronger than any other known material.

Carbon nanotubes are currently being proposed for numerous applications,such as, for example, catalyst supports in heterogeneous catalysis, highstrength engineering fibers, sensory devices and molecular wires for thenext generation of electronics devices.

There has been particularly intense study of the electrical propertiesof nanotubes, and their potential applications in electronics. Metalliccarbon nanotubes have conductivities and current densities that meet orexceed the best metals; and semiconducting carbon nanotubes havemobilities and transconductance that meet or exceed the bestsemiconductors.

Carbon nanotubes are grown by combining a source of carbon with acatalytic nanostructured material such as iron or cobalt at elevatedtemperatures. At such temperatures, the catalyst has a high solubilityfor carbon. The carbon links up to form graphene and wraps around thecatalyst to form a cylinder. Subsequent growth occurs from the furtheraddition of carbon.

Current methods of producing carbon nanotubes yield aggregations ofnanotubes. Such aggregations are referred to as bundles (or ropes).Bundles typically range in diameter from about 20 nm to 300 nm. Eachnanotube in a bundle has its own individual physical properties. Forexample, the electric property of any given nanotube in a bundle mayvary from the extremes of superconducting to insulating. Different enduse applications of nanotubes require particular physical properties.Accordingly, it is critical to be able to isolate individual nanotubesand determine their physical properties. Also, the manipulation andtailoring of individual nanotubes are necessary for end useapplications. To these ends, methods of exfoliating bundles bydissolving bundles in solvents have been explored.

Raw carbon nanotubes are essentially insoluble in organic and aqueoussolvents. Current methods of increasing the solubility of nanotubes areby the derivatization of the nanotubes. For example, acid-shortenedcarbon nanotubes which have been derivatized with thionyl chloride andoctadecylamine were shown to be soluble in several organic solvents(Chen et al. Science 282:95 (1998)). Solubilization has also beenachieved by attaching tubes to highly solublepoly(propionylethylenimine-co-ethylenimine) (Riggs et al. J. Am. Chem.Soc. 122:5879 (2000)). Sidewall derivatization with fluorine and alkanesalso appears to render tubes soluble in a number of different organicsolvents including chloroform and methylene chloride (Boul et al. Chem.Phys. Lett. 310:367 (1999)). Recently, water solubilization has beenachieved by derivatization of carbon nanotubes with glucosamine and gumarabic (Bandyopadhyaya et al. Nano Lett. 2:25 (2002)).

The current methods for exfoliating carbon nanotube bundles, and forincreasing the solubility of nanotubes, involve time-consuming, complexprocesses. Also, the range of solvents in which increased solubility hasbeen achieved, and the degree of solubility achieved, are limited.Moreover, current methods of derivatization of nanotubes, in particularsidewall derivatization, destroy the structural integrity of nanotubes,thereby potentially interfering with desirable physical properties. Forexample, the electrical properties of nanotubes may be eliminated uponsuch derivatization. These shortcomings of current methods presentobstacles for actualizing the utility of carbon nanotubes for end useapplications. Moreover, the derivatized nanotubes provided by currentmethods would require additional synthetic steps in order to use thenanotubes in catalysis or as catalytic supports.

Accordingly, there remains a need for a simple method of exfoliatingcarbon nanotubes. Also, there is a need for carbon nanotubes whichexhibit a high degree of solubility in a wide range of solvents.Moreover, for various end use applications, there remains a need for amethod of increasing the solubility of nanotubes without interferingwith their intrinsic physical properties.

SUMMARY OF THE INVENTION

The present invention provides adducts comprising a carbon nanotube anda transitional metal coordination complex. A metal of the complex isattached by a covalent linkage to at least one oxygen moiety on thenanotube. Preferably the covalent linkage is a coordinative linkage.

The oxygen moiety on the nanotube is a carboxyl group, a hydroxyl group,an aldehyde group or a ketone group. Preferably, the transitional metalcoordination complex is a Wilkinson's complex, [Ag(NH₃)₂]⁺,[Cu(NH₃)₄]²⁺, [Fe(CN)₆]⁴⁻, [Fe(CN)₆]³⁻, [Co(NH₃)₆]³⁺, [Pt(NH₃)₂Cl₂],[Cr(ethylenediamine)₃]³⁺, [Pt(NH₃)₄]²⁺, Fe(C₅H₅)₂, Ni(C₅H₅)₂, [PdCl₄]²⁻,Cr(CO)₆, [Ni(NH₃)₆]²⁺, [CoF₆]³⁻, [Pt(ethylenediamine)₂Cl₂]Br₂, [Co(NH₃)₄(SCN)Br]CI, [Fe(H₂O)₆]³⁺, [CeCl₆]²⁻, [La(acetylacetone)₃ (H₂O) 2],[Nd(H₂O)₉]³⁺, [Er(NCS)₆], [Lu(2,6-dimethylphenyl)₄]⁻,[Ho(tropolonate)₄]⁻. or mixtures thereof. The transitional metal can bein the form of a nitrate, a halide, or a salt.

The adducts have high degree of solubility in organic or aqueoussolvents. Examples of organic solvents includedimethylsulfoxide (DMSO),tetrahydrofuran (THF) or dimethylformamide (DMF). methanol, ethanol,2-propanol, acetone, o-dichlorobenzene (ODCB), dimethylsulfoxide (DMSO),tetrahydrofuran (THF), ethyl acetate, benzene and dimethylformamide(DMF).

The invention also provides methods of producing a plurality of carbonnanotubes with increased solubility. The method comprises adding asolution comprising a transitional metal coordination complex to acarbon nanotube dispersion to form a resultant dispersion comprisingcarbon nanotube-metal adducts. Fifty to 99 wt % of the carbonnanotube-metal adduct dispersion comprises nanotubes. The method canfurther comprising precipitating the adduct from the solution.

The invention also provides a method of catalyzing a reaction of anunsaturated hydrocarbon. The method comprises providing a catalystsystem comprising a carbon nanotube-transitional metal coordinationcomplex adduct in an organic solvent; and contacting a reactant and anunsaturated hydrocarbon with said catalyst system. After catalysis, theadduct can be recovered from the catalyst system.

The reaction which can be catalyzed with the system include ahydrogenation, a hydroformylation, an epoxidation, an olefin metathesis,a hydrosilylation, and an alkene (Ziegler-Natta) polymerization.

The invention also provides a catalyst support comprising a plurality ofthe adducts.

The invention also provides a method of exfoliating a plurality ofcarbon nanotube bundles, comprising contacting a carbon nanotubedispersion with transitional metal coordination complexes.

The present invention also provides an adduct comprising a carbonnanotube and a macrocyclic molecule. The macrocyclic molecule can be acoronand, a corand, a cryptand, a spherand, a cryptaspherand, ahemisspherand, a podand, a cavitand, a carcerand, and derivativesthereof.

The macrocyclic molecule forms a cavity which is about 0.5 to 10Angstroms. In one embodiment, within the cavity is a metal ion, such as,a lithium ion, a potassium ion, a calcium ion, a mercury ion, a zincion, a strontium ion, and a magnesium ion.

The macrocyclic molecule and said carbon nanotube can be covalentlylinked, or ionically linked to one another.

The macrocyclic molecule adduct have a high degree of solubility in anorganic solvent or an aqueous solvent. Examples of such organic solventinclude methanol, ethanol, 2-propanol, acetone, o-dichlorobenzene(ODCB), dimethylsulfoxide (DMSO), tetrahydrofuran (THF), ethyl acetate,benzene and dimethylformamide (DMF).

The invention also provides a method of producing a plurality of carbonnanotubes with increased solubility. The method comprising providing aplurality of carbon nanotubes in the form of bucky paper; and dispersingthe bucky paper in a solution of macrocyclic molecules. The macrocyclicmolecule solution can comprise a mixture of different macrocyclicmolecules.

The invention also provides a method of exfoliating a plurality ofcarbon nanotube bundles. Bucky paper is contacted with a solutioncomprising functionalized macrocyclic molecules.

The nanotube adducts, and methods of making the same, of the presentinvention provide several advantages over the current technology.

For example, unlike current methods of exfoliating carbon nanotubesbundles which involve complicated, time-consuming processes, the presentinvention provides methods of exfoliating nanotube bundles by simplechemical processes. Also, unlike prior art derivatized nanotubes, thenanotubes adduct of the present invention exhibit increased solubilityin a wide variety of aqueous and organic solvents. Moreover, unlikeprior art derivatized nanotubes, in one embodiment of the presentinvention, the nanotubes adducts have metallo-organic chemistry. Suchchemistry allows for the use of the adducts, without further syntheticsteps, in catalysis and as catalytic supports.

For a better understanding of the present invention, reference is madeto the following description, taken in conjunction with the accompanyingdrawings, and the scope of the invention set forth in the claims.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1. (a) Scanning electron micrograph (SEM) of unpurified, pristinenanotube bundles. Scale bar represents 700 nm. (b) TEM of a purifiedsingle-walled carbon nanotube bundle. The scale bar denotes 30 nm. (c)TEM image showing exfoliation of nanotubes (functionalized withWilkinson's complex) into smaller bundles and individual tubes. Scalebar is 30 nm FIG. 2: Selected regions of background subtracted powderX-ray diffraction spectra of (a) functionalized nanotubes and (b) asprepared raw nanotubes from 2θ values of 5-20°. The reflections can beindexed to a two-dimensional triangular lattice. The 10 peak is shiftedfrom 2θ˜5.43° (raw tubes) to 2θ˜5.92° upon derivatization. Broadening ofthe peak is also observed. The inset shows the entire diffractionspectra for 2θ values of 5-70° for raw tubes and functionalized nanotubeadducts, respectively. The Ni—Co (100) and (200) peaks are absent in thefunctionalized sample. The retention of lattice peaks indicates that thetubes are able to assemble as bundles on solvent removal.

FIG. 3. Atomic force microscopy (AFM) height images of functionalizednanotube adducts. Scale bars are (a) 500 nm, (b) 100 nm, and (c) 200 nm.(a) A high density of tubes has been deposited from solution. Aggregatesof tubes are exfoliating into smaller bundles. (b) Image of a singlebundle, approximately 15 nm in, diameter. (c) A 3-D view of exfoliatingtubes. The bundles and tubes are relatively clean and free ofnanoparticulate matter.

FIG. 4: ¹H and ³¹PNMR spectra of functionalized nanotubes at differentconcentrations and controls. Parts (a-c) are ¹H NMR spectra, while parts(d-f) are ³¹P NMR spectra. All spectra have been taken in d₆-DMSO at 298K. (a) A saturated solution of SWNT-Wilkinson's compound adduct. (b) A40% dilution of the saturated nanotube-Wilkinson's adduct solution from(a). (c). Wilkinson's compound, Rh(PPh₃)₃Cl. (d-f) are the corresponding³¹PNMR spectra for solutions (a-c), respectively.

FIG. 5: UV-visible electronic spectra of Wilkinson's complex and offunctionalized nanotubes, corrected for solvent. (a). Wilkinson'scomplex in DMSO. (b). Wilkinson's complex in CH₂Cl₂. (c). Wilkinson'scomplex diluted with 0.1 M PPh₃ in DMSO by a factor of 2. (d). Solution(a) diluted with PPh₃ in DMSO by a factor of 4. (e). SaturatedSWNT-Wilkinson's complex adduct solution in DMSO. (f-j). Successivedilutions of solution (e) with either DMSO or 0.1 M PPh₃ in DMSO.Concentration factors are 40, 20, 16, 10, and 4%, respectively. Bothtypes of solvent dilutions yield the same absorbance data in this regionof the spectrum. Inset shows a plot of absorbance at 500 nm vs.increasing dilution of the functionalized SWNT-Wilkinson's complexadduct solution with either neat DMSO or 0.1 M PPh₃ in DMSO.

FIG. 6: Near-IR spectra of pristine nanotubes and functionalizedSWNT-Wilkinson's complex adduct in DMSO. Spectra of a saturatedSWNT-Wilkinson's adduct solution as well as a 40% dilution of thissaturated solution are shown. The area of the spectrum omitted consistsof high solvent absorbances.

FIG. 7:. (a). Fluorescence emission spectra of functionalized nanotubesin DMSO solution upon excitation at 315, 350, 385, 400, 440, 500, 520,and 600 nm (from left to right), respectively. Note the excitationwavelength dependence of the emission maxima. Emission spectra show finestructure on excitation <385 nm. The emission peaks and presence ofshoulders in the band in the 600-700-nm region correspond to the firstemission band of metallic SWNTs. (b). Emission spectra upon excitationat 385 nm of a functionalized SWNT-Wilknson's complex adduct solution inDMSO, diluted with acetone and methanol.

FIG. 8. NMR spectroscopy of functionalized adducts. ¹H NMR data: (a) CE(2-(aminomethyl)-18-crown-6 ether) in deuterated methanol. (b) SWNT-CEadduct. Inset: ⁷Li NMR data. (i) CE-Li⁺ complex, (ii). SWNT-CE-Li⁺complex adduct. (iii) LiCl standard.

FIG. 9. Optical characterization of functionalized adducts. (a) Mid-IRof the SWNT-CE adduct. (b) Emission spectra of CE(2-(aminomethyl)-18-crown-6) and functionalized SWNT-CE adduct. (c)Excitation spectrum of SWNT-CE adduct.

FIG. 10: A diagram showing that the SWNT-CE adduct likely arises from azwitterionic interaction between a protonated amine on CE and anoxyanion from a carboxylic acid group, creating a COO⁻NH₃ ⁺ ionic bond.

FIG. 11: Three-dimensional AFM height image of functionalized SWNT-CEadduct bundles, adsorbed onto a flat mica substrate.

DETAILED DESCRIPTION OF THE INVENTION

An adduct of the present invention comprises a carbon nanotubecovalently linked, such as coordinatively linked, to at least onetransitional metal coordination complex, or a carbon nanotube attachedto at least one macrocyclic molecule.

The carbon nanotubes of the adducts comprise graphene in cylindricalform. The nanotubes preferably have open ends. Alternatively, thenanotubes can have one or two hemispherical caps on their ends. Inaddition to the hexagonal carbon rings of graphene, the caps cancomprise pentagonal rings of carbon. The carbon nanotube can be asemi-conducting nanotube or a metallic nanotube. (A metallic nanotubehas no band gap.) The carbon nanotube can be either single-wallednanotubes (SWNTs) or multi-walled nanotubes (MWNTs). A SWNT comprisesonly one nanotube. A MWNT comprises more than one nanotube each having adifferent diameter. Thus, the smallest diameter tube is encapsulated bya larger diameter tube, which in turn, is encapsulated by another largerdiameter nanotube.

SWNTs typically have a diameter of about 0.7 to about 2.5 nm, and alength of up to about one mm. MWNTs typically have a diameter of about 3to about 30 nm, and a length of up to about one mm.

SWNTs and MWNTs are produced, typically, as bundles. A bundle comprisesa plurality of SWNTs or MWNTs. The diameter of a bundle of SWNTs istypically about 10 to 20 nm. The diameter of a bundle of MWNTs istypically about 2.5 to 250 nm.

The carbon nanotubes can be prepared by methods known in the art. Forexample, carbon nanotubes can be prepared by the laser vaporization.(Thess et al. Science 273: 483 (1996)). Also, carbon nanotubes can beprepared by arc discharge (Ishigami, M. et al. Chem. Phys. Lett. 319:457(2000); Su, M. et al. Chem. Phys. Lett. 322:321 (2000); Journet, C. etal. Nature 388:756 (1997); Colbert et al. Science 266:1218, (1994));Shi, Z. et al. Carbon 37:1449 (1999) and Ebbeson, T. et al. Nature358:220 (1992)). The carbon nanotubes can be prepared by catalyticchemical vapor deposition (Kukovitsky, E. F. et al. Chem. Phys. Lett.317:65 (2000); Su, M. et al. Chem. Phys. Lett. 322:321 (2000); Li et al.Science 274:1701 (1996); and Pan, Z. et al. Chem. Phys. Lett. 299:97(1999)).

The carbon nanotubes may optionally be doped with other elements, forexample, with metals, such as boron or nitrogen; or gases, such asammonia and oxygen, by methods known in the art.

In one embodiment, an adduct of the present invention comprises a carbonnanotube and a transitional metal coordination complex. The metal of thecoordination complex can be any transitional metal. Transitional metalsinclude elements 21 through 29 (scandium through copper), 39 through 47(yttbrium through silver), 57 through 79 (lanthanum through gold), andall known elements from 89 (actinium) on.

Preferred examples of transitional metal coordination complexes includeRhCl(PPh₃)₃ (also known as the Wilkinson's complex, wherein Ph standsfor phenyl), [Ag(NH₃)₂]⁺, [Cu(NH₃)₄]²⁺, [Fe(CN)₆]⁴⁻, [Fe(CN)₆]³⁻,[Co(NH₃)₆]³⁺, [Pt(NH₃)₂Cl₂], [Cr(ethylenediamine)₃]³⁺, [Pt(NH₃)₄]²⁺,Fe(C₅H₅)₂, Ni(C₅H₅)₂, [PdCl₄]²⁻, Cr(CO)₆, [Ni(NH₃)₆]²⁺, [CoF₆]³⁻,[Pt(ethylenediamine)₂Cl₂]Br₂, [Co(NH₃)₄ (SCN)Br]Cl, [Fe(H₂O)₆]³⁺,[CeCl₆]²⁻, [La(acetylacetone)₃ (H₂O) 2], [Nd(H₂O)₉]³⁺, [Er(NCS)₆],[Lu(2,6-dimethylphenyl)₄]⁻, [Ho(tropolonate)₄]⁻. Nitrates, halides, orsalts of transition metals also can be used.

The metal of the complex is attached to at least one oxygen moiety,i.e., oxygen functional group, on the nanotube by a covalent linkage.Oxygen moieties include a carboxyl, a hydroxyl, an aldehyde or a ketonefunctional group.

A covalent linkage is the sharing of electrons by a pair of atoms. Thecovalent linkage can be via a single bond, i.e. one pair of electronsshared, or a double bond, i.e. two pairs of electrons shared.Preferably, the covalent linkage is a coordinative linkage. Acoordinative linkage comprise a pair of electrons donated by only one ofthe two atoms that are joined. The covalent linkages can also be polarcovalent bonds (hybrid bonds). Such bonds are partially ionic in nature;that is, the electrons are not shared equally.

Transitional metals exhibit a variety of oxidation states. Depending onthe particular metal used in an adduct, the oxidation states of a metalin the adduct can vary from +1 to +7. For example, in the embodimentwherein the metal complex is a Wilkinson's complex, the oxidation stateof rhodium within an adduct is preferably three or two. As anotherexample, in the embodiment wherein the metal complex is [Pt(NH₃)₄]²⁺,the oxidation state of platinum within an adduct is preferably two orfour.

The spatial arrangement of a particular adduct can be, for example, atetracoordinate structure, pentacoordinate structure, a hexacoordinatestructure, septacoordinate structure, octacoordinate structure etc. Thearrangement depends upon the particular transitional metal complex, thenumber of ligands held by the metal, and the number of attachments themetal makes with the nanotube. For example, in the embodiment in whichthe Wilkinson's complex is used, preferably the adduct has ahexacoordinate structure.

An adduct can comprise one or more than one transitional metal complex.The number of metal complexes attached is governed by the quantity ofoxygen moieties on the surface of a nanotube. About 3 to 4% of thecarbon atoms on a nanotube have oxygen moieties. Of these moieties, allor about one third, for example, has a metal complex attached. In oneembodiment, an adduct can comprise a mixture of different types of metalcomplexes.

The adducts of the invention exhibit a high degree of solubility inorganic or aqueous solvents. That is, a plurality of adducts readilydissolve in solvents, and remain dissolved upon prolonged standing. Forthe purposes of this specification, prolonged standing includes standingfor several hours, several weeks, several months, or standing for anindefinite period of time. As the quantity of metal complexes on ananotube increases, the solubility of the nanotube increases.

Examples of organic solvents in which solubility is increased includedimethylsulfoxide (DMSO), tetrahydrofuran (THF), dimethylformamide(DMF), methanol, ethanol, 2-propanol, acetone, o-dichlorobenzene (ODCB),ethyl acetate, and benzene.

For example, a adduct comprising a Wilkinson's complex exhibits asolubility of greater than 250 mg/L in DMSO, and a solubility of greaterthan 75 mg/L in THF or DMF.

Also, the adducts exhibit strong intrinsic luminescence when placed inan organic solvent.

In another aspect, the present invention provides methods of making thenanotube-metal complex adducts described above.

The production of the adducts of the present invention are preferablybased on the presence of oxygen functional groups on a nanotube by whichto allow the covalent linkage with a transitional metal complex. Theoxygen functional groups can be anywhere on the outer surfaces of thenanotubes. Preferably, the groups are at the tips of open-endednanotubes.

During the formation of a carbon nanotube, oxygen moieties can arise onthe nanotube. In another embodiment, carbon nanotubes with oxygenmoieties are produced by oxidation processes. Alternatively, carbonnanotubes with oxygen moieties are obtained from an outside source.

Processes for oxidizing nanotubes are well known in the art. Forexample, raw SWNT bundles can be oxidized according to existingprocedures involving acidic potassium permanganate solution andhydrochloric acid. See for example Hiura et al. Adv. Mater 7:275 (1995).Also, for example, MWNT samples prepared via arc discharge can bepurified by oxidizing the carbon nanotubes at 700° C. in the presence ofair until approximately 2% of the original mass remained. SWNT samplescan be prepared via arc discharge, pulsed laser vaporization, orchemical vapor deposition. The SWNT samples can be purified bysonication and filtration through 0.8 micron pore membranes. See forexample, Bonard et al. Adv. Mat.,9, 827 (1997), K. Tohji et al. J. Phys.Chem. B, 101, 1974 (1997), and K. Tohji et al., Nature, 383, 679,(1996).

Optionally, the carbon nanotubes can be shortened. Techniques by whichto shorten nanotubes include acid etching, ion beam milling, ballmilling, and gas etching.

The nanotubes, which comprise oxygen moieties, are placed in an organicsolvent to form a carbon nanotube dispersion. Preferably, the organicsolvent is, for example, DMSO, THF or DMF. The dispersion may optionallybe sonicated. To this dispersion is added a solution comprisingtransitional metal coordination complexes to form a resultantdispersion. The complexes are as described above. In one embodiment, thetransitional metal coordination complex solution can comprise a mixtureof different complexes.

Preferably, the addition of the metal complex solution to the carbonnanotube dispersion takes place in an inert atmosphere at roomtemperature. The addition is preferably effected in a gradual fashion,for example, in a dropwise fashion. During the addition, the resultantdispersion is preferably stirred vigorously. Once the addition iscomplete, the resultant dispersion is preferably stirred forapproximately a day, more preferably two days, most preferably for threedays, and optimally for four days at an elevated temperature. Theelevated temperature is preferably about 40 to 75° C., more preferablyabout 50 to 65° C., and most preferably about 55 to 60° C.

The resultant dispersion comprises carbon nanotube-metal complexadducts, as described above. Preferably, the resultant dispersioncomprises from about 50 to 99 wt % of carbon nanotubes, more preferablyfrom about 80 to 99 wt % of carbon nanotubes, and most preferably fromabout 96 to 99 wt % of carbon nanotubes.

In one embodiment, the adducts are recovered from the resultantdispersion. Preferably, recovery is effected by precipitating the adductfrom the solution by the addition of a salt solution, such as, forexample, and aqueous sodium chloride solution. Recovery can also beeffected by the addition of liquid which is nonsoluble in the resultantdispersion. For example, a solvent or solution could be added that wouldpreferentially dissolve the adduct or the products of the reaction, suchthat the catalyst can be separated from the product.

While not wishing to be bound by theory, it is believed that the factthat the tubes can be precipitated out upon the addition of a saltsolution suggests that the tubes are charged to some extent in solutionand that the observed solubility occurs by means of electricdouble-layer stabilization. The presence of charge likely originates incarboxylate anion-like species, formed during the purificationprocedure, coordinating to the metal of the complexes.

In one aspect of the present invention, a plurality of the adducts canbe used as catalyst systems. In particular, the nanotubes of the adductssupports, and immobilizes, transitional metal complexes, wherein thecomplexes function as catalysts. The catalyses effected by the catalystsystems can be carried out at room temperature.

Depending upon the particular complex used in the adducts, the catalystsystems can catalyze various reactions. For example, the catalyst systemcan be used to catalyze any reaction of an unsaturated hydrocarbon.Examples of such reactions include hydrogenation, hydroformylation,epoxidation, olefin metathesis, hydrosilylation, and alkene(Ziegler-Natta) polymerization. These reactions are well known in theart. Some of the transitional metal complexes need to be modified inorder to perform some of the catalytic reactions, as is well known to askilled artisan. For example, changing a single triphenylphosphineligand to a CO on the Wilkinson's complex would result in ahydroformylation vis-à-vis a hydrogenation.

Further guidance on catalytic reactions can be found in Cotton, F. A.;Wilkinson, G., Murillo, C. A., Bochmann, M., Advanced InorganicChemistry, John Wiley and Sons (New York), 1999; Crabtree, Robert,Organometallic Chemistry of the Transition metals, John Wiley and Sons(New York), 2000; and Miessler, G. L. and Tarr, D. A., InorganicChemistry, Prentice Hall (New Jersey), 1991.

Examples of unsaturated hydrocarbons include alkenes, acetylene,alkadienes, cycloolefins, cycloacetylene, cycloalkenes, alkynes,cyclohexene or aromatic compounds.

In one embodiment, the catalyst systems allow for homogeneous catalysis;that is, the reactants and the metal complex catalyst are all in thesame phase. In this embodiment, the catalyst system comprises a carbonnanotube-transitional metal coordination complex adduct in an organicsolvent. The organic solvent can be any organic solvent or mixture ofsolvents, including, for example, the organic solvents listed above.Preferred examples of organic solvents include halogenated organicsolvents. An example of a halogenated organic solvent is CHCl₃.

Most unsaturated hydrocarbons are in a liquid phase, and are introducedinto the catalyst system along with other liquid reactants, such ashydrides. Alternatively, hydrogen can be introduced as hydrogen gas. Thehydrogen gas dissolves into the solvent. Once catalysis is complete, theadducts can be recovered from the catalyst system. The recovery cancomprise precipitating the adduct from the catalyst system by theaddition of a high-ionic strength solution, i.e. a salt solution.

In an alternative embodiment, the catalyst system is a solid statesystem; that is, the system is not in solution. In such embodiment, thereactants in the gas phase are flowed over the nanotube-metal complexadducts. In particular, some unsaturated hydrocarbons are in the gasphase, such as, for example, some of the lower olefins. Such olefinsalong with hydrogen gas are flowed over the catalyst system.

In another aspect of the invention, a method of exfoliating a pluralityof carbon nanotubes, is provided. Exfoliation is the separation,isolation or dispersing of a plurality nanotubes, i.e. nanotube bundles,into either smaller bundles or into single nanotubes.

In this aspect, a carbon nanotube dispersion is contacted with asolution comprising transitional metal coordination complexes. Thenanotube dispersion comprises a plurality of nanotube bundles whereinthe bundles have an average first diameter. Upon addition of atransitional metal coordination complex solution, the bundles areexfoliated. The exfoliated bundles have an average second diameter. Theaverage second diameter is 10-80% or 30-50% of the average firstdiameter. The exfoliated bundles have an average diameter of 15 to 20nm. About 30% to 70% of the nanotubes in the original dispersion areexfoliated to a single nanotubes.

While not wishing to be bound by theory, it is believed that the bulkymetal complexes spread along the length of carbon nanotubes, lead todisruption of the molecular interactions between the nanotubes, therebycausing the nanotubes to stay apart in solution. In fact, the metalcomplexes essentially substitute for the pre-existing intertube andinter bundle van der Waals interactions, and provide for a favorableinterface to the solvent.

Another aspect of the invention is a method of providing single carbonnanotubes, and carbon nanotube bundles with a selected diameter. In thisaspect, a carbon nanotube dispersion is contacted with a solutioncomprising a transitional metal coordination complex to form a resultantdispersion. Adducts are preferentially formed with small bundles andwith single nanotubes. For the purposes of this specification, a smallbundle has a diameter of less than about 10 nanometers. The adducts arethen precipitated from the resultant dispersion.

In another embodiment of the present, an adduct comprises a carbonnanotube and a macrocyclic molecule. The macrocyclic molecule can be anymacrocyclic molecule. Preferably, a functional group attaches themacrocyclic molecule to the nanotube.

Examples of macrocyclic molecules include coronands, such as crownethers; corands (modified crown ethers); cryptands; spherands;cryptaspherands; hemisspherands; podands; cavitands, carcerands andderivatives thereof. All these structures have cavities that are 0.5 to10 Angstroms in diameter.

Coronands, cryptands, corands, podands and cavitands act as hosts ofguest entities, i.e. anions, cations or neutral species. The guestsdefine cavities within the molecules, and bind within the cavities.

A coronand is a macrocyclic molecule which has only one ring, thus onecavity. A coronand comprises any type of heteroatom. Examples ofheteroatoms include sulfur atoms, oxygen atoms and nitrogen atoms. Acrown ether is a coronand which comprises only oxygen heteroatoms in thering.

The cavity size of crown ethers is determined by the coordination numberof the ether and the size of a guest, i.e. a metal ion. Preferably, thecavity size of the crown ethers used in the adducts range from about0.99 to about 8.05 Angstroms in diameter; more preferably the diametersrange from about 1.7 to 3.9 Angstroms. For example, a 18-crown-6 has adiameter range from 2.6 to 3.5 Angstroms. The diameter values arederived from CPK (Corey-Kuhn-Pauling) molecular models, as would beknown by a skilled artisan.

Preferably, the rings of the crown ethers of the adducts have about 12to 60 atoms; more preferably, the rings have about 15 to 44 atoms.Preferably, the rings of the crown ethers have about 3 to 20 oxygenatoms. More preferably, the rings have about 5 to 11 oxygen atoms.

Examples of crown ethers for use in the adducts include 12-crown-4,15*crown-5,18-crown-6,27-crown-9,30-crown-10, anddicyclohexano-18-crown-6.

A corand is a modified crown ether, such as a crown ether with pendantgroups. Examples of pendant groups include alkyl groups, ether groups,keto groups, amine groups, ester groups, carboxyl groups and thiolgroups.

A cryptand is a macrocyclic molecule which has two or more rings andcontains any type of heteroatom. Cryptands can be defined by theirnumber of binding sites. Preferably, the crytands in the nanotubeadducts have about 5 to 15 binding sites. Examples of cryptands for usein the adducts include Cryptand 2.2.1, Cryptand 2.2.1 Noxacryptand3.3.3, Cryptand 2.2.2, Oxacryptand 3.3.3, Oxacryptand 3.3.4, andDimethyloxacryptand 3.3.4. The numbering represents the number of donorheteroatoms on each branch.

A podand is an open chain molecule with two or more binding sites. Basedon the number of arms a podand has, the molecule can be classified as amono, di, and tri podand. Each of the arms bears an ‘n’ number of donoratoms to bind to a guest. Preferably, the podands in the nanotubeadducts have about 1-4 arms wherein each arm has about 2 to 10 donoratoms. Preferred examples of podands include 1,10-Dimethyl<O₄podand-4>,<(8)Quinolino, O₅(8)quinolinopodand-7>, and 16-Methyl-1,19-diphenyl{3}<O₂NO₂N<S(7)-podand-7>.

A cavitand is a synthetic organic compounds with enforced concavecavities large enough to bind complementary organic compounds or ions.They are named as [n] cavitands, depending on the number of repeatingunits that are cyclized (usually the same as the number of phenyl groupsin the interior rings). Preferably, the cavitands in the nanotubeadducts range from [1] cavitands to [7] cavitands. Cavitands which arevariously substituted with organic sidechains are also preferred.

A spherand is similar to crown ether and cavitands in that they havebinding sites to hold guests. However, they differ in that theirstructure is not conferred by the binding of a guest. That is, they arepreorganized ligand systems. Hence, on binding the guest, no substantialstructural reorganization is needed. The cavities of spherands are fixedand are usually spherical. The cavity sizes of the spherands for use inthe adducts can preferably range from about 1 to 8.5 Å in terms of CPKmodels.

A hemispherand and a cryptaspherand are hybrid structures. Ahemispherand is a hybrid of a spherand and a coronand. A cryptaspherandis a hybrid of a spherand and a cryptand. The cavities of thesestructures are partially preorganized ligand systems. That is, a part ofthese structures changes according to guest binding, while another partis prefigured into a particular orientation. The sizes of these hybridstructures are similar to their respective parent structures.

Carcerands are closed surface hosts with fixed-size interiors. They arelarge enough to imprison guests of the size of ordinary solventmolecules in covalently bonded cage. These are thus molecularcontainers, which trap molecules inside of them. A large number of theseare based on linking two cavitands by four linkers. The size of thesecontainers can be varied to trap various solvent molecules, such as DMFand DMSO as well as gases such as Xe and CF₄.

Examples of macrocyclic molecules used in the adducts can be found inDonald J. Cram, Nobel Lecture, University of California (Dec. 8, 1987);Donald J. Cram, Journal of Inclusion Phenomena, 6(4):397 (1988); “Crownethers and cryptands” by George W. Gokel (Royal Society of Chemistry,1991) and “Crown ethers and analogous compounds” by Michio Hiraoka(edited) (Elsevier Science, 1992).

An adduct can comprise one type of macrocyclic molecule, or differenttypes of macrocyclic molecules.

Examples of guest entities within the macrocyclic molecules includemetal ions. Preferred metal ions include, for example, a lithium ion, apotassium ion, a calcium ion, a mercury ion, a zinc ion, a strontiumion, a silver atom, a cesium atom and a magnesium ion.

In one embodiment, the macrocylic molecule and the nanotube are linkedto one another covalently. Covalent linkages are described above.Examples of covalent linkages include amide linkages, ester linkages,anhydride linkages, cysteine linkages and thioester linkages.

In another embodiment, the macrocylic molecule and the nanotube arelinked to one another ionically. For example, in one embodiment, anamino functional group is on the macrocyclic molecule and an oxygenatedmoiety is on the nanotube. In another embodiment, an amino functionalgroup is on the nanotube and an oxygenated moiety is on the macrocyclicmolecule.

While not wishing to be bound by a theory, it is believed that theattachment of the amino functional group to the oxygenated moiety is byan ionic attachment between a protonated amine and an oxyanion. (SeeFIG. 11.)

The functional group can be directly attached to the macrocyclicmolecule. Alternatively, the adduct can further comprise an organicmolecule linker between the functional group and the macrocyclicmolecule. The linker preferably comprises less than about twenty carbonatoms. Preferred examples of linkers include an ethyl group, and amethyl group. Other examples of organic molecule linkers arebifunctional amines. Examples of bifunctional amines are alkyl or aryldiamine derivatives. Examples of diamine derivatives are ethylenediamineand semicarbazide.

The macrocylic molecule adducts of the invention exhibit a high degreeof solubility in organic or aqueous solvents. That is, a plurality ofadducts readily dissolve in solvents. As the quantity of macrocylicmolecules on a nanotube increases, the solubility of the nanotubeincreases.

Examples of organic solvents in which solubility is increased includedimethylsulfoxide (DMSO), tetrahydrofuran (THF), dimethylformamide(DMF), methanol, ethanol, 2-propanol, acetone, o-dichlorobenzene (ODCB),ethyl acetate, and benzene. For example, Table 1 lists the solubilitiesof a 2-aminomethyl-18-crown-6-nanotube adducts in various solvents.TABLE 1 Concentrations of SWNTs in the Form of Solubilized2-aminomethyl-18-crown-6-nanotube Adducts for Selected Solvents^(α)Concentration of SWNTs in Solvent solubilized adduct (in mg/L) THF 270Acetone 280 DMSO 290 ODCB 300 DMF 610 Water 1100 Methanol 1600^(α)Values are within a ±10% error range.

In another aspect, the present invention provides methods of making thenanotube-macrocyclic molecule adducts described above.

In one embodiment, the production of the adducts of the presentinvention are preferably based on the presence of oxygenated moieties ona nanotube by which to allow the attachment of a macrocyclic molecule.The oxygenated moieties can be anywhere on the outer surfaces of thenanotubes. Preferably, the oxygenated moieties are at the tips ofopen-ended nanotubes. Methods to obtain, and form such nanotubes aredescribed above.

A plurality of carbon nanotubes, which have carboxyl and/or hydroxylfunctional groups, are provided in the form of bucky paper. Bucky paperis a free standing film comprising bundles of nanotubes. The bucky paperis ground up and dispersed in liquid macrocyclic molecules, or inmacrocyclic molecules in solution, to form a resultant dispersion. Themacrocyclic molecules are as described above. In one embodiment, thesolution can comprise a mixture of different macrocyclic molecules. Theratio of the amount of bucky paper to the amount of macrocyclicmolecules varies depending upon the specific macrocyclic molecules used.As an example, in the embodiment wherein the macrocylic molecule is a2-aminomethyl-18-crown-6-ether, the ratio of the crown ether to thebucky paper is about three to one.

The resultant dispersion comprises a plurality of nanotube-macrocyclicmolecule adducts. The resultant dispersion has a highly viscousconsistency, and can be referred to as black paste. The resultantdispersion preferably comprises from about 50 to 99 wt % of carbonnanotubes, more preferably from about 80 to 99 wt % of carbon nanotubes,and most preferably from about 96 to 99 wt % of carbon nanotubes.

Preferably, during the production of the adducts, the black paste ispurified. For example, the black paste can be mixed with distilleddeionized water. The mixture can then be swirled, sonicated, and allowedto stand for about a few minutes to few hours. Preferably, afterstanding, distilled water can again be added followed by vigorousstirring.

In one embodiment, the adducts are recovered from the resultantdispersion. Preferably, recovery is effected by precipitating theadducts from the solution by the addition of a high ionic strengthsolution, such as, for example, a salt solution.

While not wishing to be bound by theory, it is believed that the factthat the tubes can be precipitated out upon the addition of a high ionicstrength solution suggests that the tubes are charged to some extent insolution and that solubility occurs by means of electric double-layerstabilization.

In another embodiment, the oxygenated moiety is on the macrocyclicmolecule. In this embodiment, any oxygenated moiety on the nanotube isconverted to a functional group which would react with the oxygenatedmoiety on the macrocyclic molecule, such as, for example, an aminogroup.

In another embodiment, any of the following functional groups can beeither on the nanotube or macrocylic molecule: an amino group, a ketogroup, an aldehyde group, an ester group, an hydroxyl group, a carboxylgroup, or a thiol group. The functional group on the macrocyclicmolecule is required to reactive with the functional group on thenanotube. If the two groups are not reactive with each other, anappropriate bifunctional linker can be used, as would be known by askilled artisan.

In another aspect of the invention, a method of exfoliating a pluralityof carbon nanotubes is provided. A plurality of carbon nanotubes in theform of bucky paper is contacted with a solution comprising macrocyclicmolecules, as described above. The nanotube bundles in the bucky paperhave an average first diameter. Upon addition of the macrocyclicmolecule solution, the bundles are exfoliated. The exfoliated bundleshave an average second diameter. The average second diameter is about10-80% or 40-65% of the average first diameter. The exfoliated bundleshave an average diameter of about 30 to 200 nm. About 1 to 50% of thenanotubes in the original dispersion are exfoliated to a singlenanotubes.

The derivatization process occurs as a result of salt formationinitiated by a complementary attractive, zwitterionic interactionbetween carboxylic groups located at the ends, sidewalls, and defectsites of the oxidized SWNTs and amine moieties dangling from the sidechain of the crown ether. This so-called ionic (charge-transfer)functionalization enhances the stability of SWNT solutions byeffectively preventing nanotubes from aggregating in the solution state,though it does not necessarily prevent them from clumping together upondrying

In another aspect of the invention, methods of modifying a physicalproperty of a carbon nanotube are provided. The methods comprise formingadducts from the carbon nanotube, as dscribed above. The adductscomprise a carbon nanotube covalently linked to at least onetransitional metal coordination complex, or a carbon nanotube attachedto at least one macrocyclic molecule.

The physical property which is modified is, for example, electronicproperties, electrical properties, electromechanical properties, opticalproperties, chemical properties, mechanical properties, structuralproperties, thermal properties and thermoelectric properties.

The electrical property which is modified can be, for example,conductance, resistivity, carrier mobility, transport properties,permittivity, and charge transfer properties. The modification ofconductance can be, for example, a tunability in conductance.

The structural property which is modified can be, for example,elasticity, and ease of composite formation.

In another aspect of the invention, a device comprising the adducts ofthe invention is provided. The device can be, for example, sensors, adevice used in molecular electronics, solar cells, a device used inoptoelectronics, a device used in nanocatalysis, and scanning probemicroscopy tips.

EXAMPLES

Adduct Comprising Carbon Nanotube and Wilkinson's Complex

Nanotube Synthesis and Purification. Raw SWNTs (FIG. 1 a) were producedby the laser oven method (Carbolex, Lexington, Ky.), and individualtubes have a reported mean diameter of 1.41 nm, although experimentally,a large distribution of diameters was observed. The raw SWNT materialcontains about 30 wt % of metal catalysts, such as Ni and Co. To purifythese materials, the SWNTs were oxidized according to existingprocedures by an acidic KMnO₄ solution's and then washed thoroughly withHCl and water. Carboxylic acid groups are expected to be the predominantspecies on the opened caps and defect sites. SEM (FIG. 1 a) and TEM(FIG. 1, b and c) results showed that the oxidation process not onlyremoved most of the amorphous carbon but also the majority of the metalparticles; furthermore, X-ray diffraction data (FIG. 2, inset) indicatedthe disappearance of the catalyst-related (100) and (200) peaks of cubicNi and Co for posttreated tubes. The purified tubes were then dried at100° C. and redispersed in DMSO by mild sonication (20 s).

Generally, solvents, such as dimethylformamide and tetrahydrofuran(Acros Fisher), were used after distillation and were stored over 4 Åmolecular sieves. All other reagents were obtained commercially and usedwithout further purification.

Synthesis of SWNT-Wilkinson's Adduct. In a typical synthesis, thereaction was carried out in a Schlenk setup. To a briefly sonicatednanotube dispersion in DMSO was added, dropwise, 10 mL of a 10 mMsolution of Wilkinson's catalyst in DMSO solution under vigorousstirring, in an inert Ar atmosphere. The reaction mixture was thenstirred at 55-60° C. for a period of 80 h. It was observed that asubstantial portion of the nanotubes dissolve into a visually,nonscattering solution. The reaction mixture was filtered over a 0.2-μmNylon membrane, after which undispersed chunks of unreacted bucky paperwere removed, and the remaining solid was then successively washed withDMSO, ethanol, and water.

The dissolved tubes in solution could be salted or precipitated out byadding in a saturated aqueous NaCl solution. These were purified byfiltering over a 0.2-μm Nylon membrane and washing in an analogousmanner as previously described. In terms of solubility behavior, thesynthesized adducts could be readily redissolved in DMSO by mildstirring, demonstrating the reversibility of the dissolution process,and the resultant product was stable, even after four months. Theproduct is not particularly air-sensitive, but if left out in theambient atmosphere for extended periods of time, oxidation of some ofthe triphenylphosphine groups to triphenylphosphine oxide is inevitable.Dissolution of the adducts in THF and DMF was also observed, but thederivatized tubes tended to precipitate out of solution within a day.

Catalysis with SWNT-Wilkinson's Adduct. The adduct-mediatedhydrogenation reaction of cyclohexene was carried out in a DMSO/CHCl₃mixed solvent system by bubbling in a mixture of hydrogen gas in argonunder Schlenk conditions for a period of 3 days at room temperature.Typically, 1 mL of a saturated solution of the supported catalyst inDMSO was stirred with 3 mL of CHCl₃ and 3 mL of cyclohexene. Thereaction was monitored by ¹H NMR spectroscopy through the appearance ofcyclohexene peaks at ˜1.52 ppm. The reaction yield obtained wasapproximately 30%, but it is expected that a higher yield is likely withfurther optimization of the solvent system and with an improvedhydrogenation apparatus. Electron Microscopy. Samples for TEM wereobtained by drying sample droplets from an ethanolic or DMSO solutiononto a 300 mesh Cu grid with a lacey carbon film. All the micrographswere taken at an accelerating voltage of 120 kV on a Philips CM 12 TEM,equipped with EDAX capabilities. SEM images were obtained on Cu grids aswell at accelerating voltages of 1-2 kV at a 2-mm working distance usinga Leo 1550 field emission instrument.

Atomic Force Microscopy. AFM height images were taken in Tapping mode inair at resonant frequencies of 50-75 kHz with oscillating amplitudes of10-100 nm. The samples were spin coated onto a mica substrate, andimaged with Si tips (k=1-5 N/m) using a Multimode Nanoscope IIIa(Digital Instruments, Santa Barbara, Calif.).

Nuclear Magnetic Resonance. Deuterated solvents, including CDCl₃,d₆-DMF, d₆-DMSO, and d₇-THF, were purchased from Aldrich and usedwithout further purification. All NMR spectra were obtained on a BrukerAC-250 multinuclear FT-NMR at 298 K. The 3 P and ¹³C NMR data wereproton decoupled. ³¹P NMR results are referenced to an externalphosphoric acid standard.

X-ray Diffraction. Powder X-ray diffraction spectra were collected on aScintag diffractometer, operating in the Bragg configuration using Cu Kαradiation (X=1.54 Å). A Soonerveld background subtraction was performedto remove low Q diffuse reflections. Parameters used for slit widths andaccelerating voltage, as well as Savitzky-Golay smoothing algorithms,were identical for all the samples.

Optical Spectroscopy. UV spectra were obtained at high resolution on aThermoSpectronics UV1 using quartz cells with a 10-mm path length. NIRspectra were obtained on a Nicolet Nexus 670 spectrophotometer with aCaF₂ beam splitter and an InGaAs room-temperature detector using a 5-mmpath length quartz cell. All spectra collected were corrected to accountfor a background of the appropriate solvent. Fluorescence data wereobtained on a Jobin Yvon Spex Fluorolog 3.22, equipped with a 450-Wxenon source and configured with double monochromators for both emissionand excitation, with a 1-s integration time, to provide for stray lightrejection while maintaining high light throughput. The experiments wereperformed using front face collection optics to collect the emissionmost efficiently.

Results

Microscopy. Electron microscopy (FIG. 1) and AFM data (FIG. 3) of thederivatized adducts indicate a high density of small bundles, of theorder of 15-20 nm in diameter (as compared with 30 nm on average forunfunctionalized tubes) and up to a few micrometers in length, as wellas individual tubes, arising from exfoliation of larger bundles. Thehigh purity of the purified starting material and the relatively largeabundance of predominantly clean nanotubes, relatively free ofparticulate impurities, in SEM and TEM images of the synthesized adductindicates that it is indeed the SWNTs, and not other extraneousimpurities, that have been derivatized and dissolved. EDAX data confirmthe presence of Rh, P, and Cl elemental signatures on the functionalizedtubes, with less than 1% loading of the functional moieties.

X-ray Diffraction. The powder XRD pattern for a solid, functionalizedadduct sample shows recovery of the nanotube lattice peaks (FIG. 2 a),indicating that the tubes are able to coalesce together upon solventremoval. The relative broadness of the 10 peak (FIG. 2 a), though, withrespect to the initial Carbolex peaks (FIG. 2 b), is consistent with thepresence of lattice mismatch induced by chemical derivatization, andmoreover, this peak also shows a shift toward higher q. The powderprofile and the position of the 10 reflection is sensitive to a numberof parameters including the size of the bundle, the tube diameter, thedistribution of these tube diameters, and the lattice constant. Hence,the broadened peak observed can be accounted for by a smaller aggregatetube bundle size, whereas the upshift in q values can be explained bythe presence of a larger quantity of smaller-diameter tubes within thefunctionalized adduct sample as compared with that of the original rawSWNT sample. A smaller tube bundle size would also be consistent withthe presence of exfoliation in solution, as suggested by the microscopydata.

NMR Spectroscopy. NMR spectroscopy confirmed the coordination of thecomplex onto the oxidized tubes. In particular, ³¹P, ¹H, and ¹³C NMRspectra of the adduct were obtained. Comparison of the ³¹P and ¹H NMRdata with that of the starting material, RhCl(PPh₃)³¹, is shown in FIG.4. FIG. 4, a and d, represents data corresponding to saturated solutionsof nanotube-adduct complexes, whereas FIG. 4, b and e, is associatedwith results at 40% saturation. There are two important featuresobserved in all of these spectra. First, there is a chemical shiftdifference of ˜3 ppm in the ³¹P NMR data between the resonances of theadduct and of Wilkinson's catalyst, consistent with the formation of aderivatized product.

Thus, the relatively small chemical shift changes observed from thestarting material to the adduct are evidence of coordination of the Rhmetal center to oxygen atoms on the tube as opposed to through directinvolvement of the phosphine ligands.

Second, as noted with other types of functionalizations performed, theNMR peaks of nanotubes tend to broaden upon derivatization. Since thelarge nanotubes move relatively slowly on the NMR time scale ofmeasurement, observed broadening of the NMR peaks is indicative of thelocalization and immobilization, through restriction of the degrees ofconformational freedom, of metal complex molecules onto the oxygenatedsurface sites of the tube with the accompanying loss of symmetry.Indeed, this same broadening trend is observed for all nuclei, including³¹P, ¹H, and ¹³C. While inhomogeneities in the local magnetic fieldinduced by the diameter and helicity-dependent diamagnetism of the SWNTsthemselves and the partial alignment of the tubes in the magnetic fieldof the NMR magnet are expected to contribute to peak broadening, in thepresent case, the broadening is likely a result not only of slowtumbling and motion of the tubes in solution, preventing rotationalaveraging, but also of a slow rate of ligand exchange upon complexationto the tubes.

Providing more evidence for the localization mechanism postulated, it isnoted that in pristine Wilkinson's complex, the loss of atriphenylphosphine moiety is facile and indeed a vital step in itscatalytic behavior. In DMSO solvent, for the starting material, exchangeinvolving triphenylphosphine takes place very rapidly, such that all thephosphines in the ³¹ P NMR spectra become equivalent (unlike in CH₂Cl₂or in benzene.), which is similar to phenomena noted at highertemperatures; also, coupling of the P nucleus to the Rh nucleus isremoved. The fact that the phosphine peaks are broadened upon theaddition of and reaction with SWNTs suggests the presence of a slowerrate of exchange and the inequivalence of the phosphine ligands. Hence,this phenomenon is steric in nature, arising from reduced accessibilityof the metal center for the phosphine ligands due to complexation withthe nanotube. Essentially, the nanotube itself can be considered as abulky, sterically encumbering ligand. Not surprisingly, on increasingthe concentration of nanotubes, the ¹H NMR spectra, like the ³¹P NMRdata, similarly broaden.

The ¹³C solution NMR spectrum for the adduct contains broad resonancescentered at δ=128.6, 128.8, 131.4, 131.5, and 132 ppm. DEPT spectraconfirmed that all these are C—H aromatic carbons, originating fromphosphine groups. No resonances were seen, however, for the nanotubecarbons. Nanotube resonances have not as yet been observed in solutionNMR studies of these materials, even upon substantial isotopicenrichment with ¹³C (up to 20 times the natural abundance). Among thereasons cited for this situation include the relatively long relaxationtimes of nanotube carbons, as well as the low concentrations ofnanotubes present, even upon saturation, which cannot be readilydetected by ¹³C solution NMR.

Optical Spectroscopy. The UV-visible spectra collected for pureWilkinson's complex, RhCl(PPh₃)₃, in DMSO show evidence of increasedpeak structure (apparent upon normalization of intensity) with theaddition of 0.01 M PPh₃, as the dissociation equilibrium is shifted tomonomeric, undissociated species. (FIG. 5) Its absorbance maximum inDMSO is red-shifted from the literature value of 361 nm in CH₂Cl₂ to 387nm. The synthesized adduct, however, has a featureless spectrum,indicating that the initial Rh(I) chromophore undergoes reduction duringthe coordination process. The optical characteristics of the adductsolution, monitored by absorbance at 500 nm, obey Beer's law withrespect to relative concentrations; the slope of thelinear-least-squares fit is then analogous to an extinction coefficient(FIG. 5, inset). The solubility of the tubes was found to be stronglydependent on the concentration of RhCl(PPh₃)₃, suggesting thatsolubilization is chemically induced. Moreover, addition of a largeexcess of PPh₃ still does not result in the appearance of a λ_(max)feature in the electronic spectrum, indicating that the adduct isprobably a Rh (III) species.

The featureless absorbance spectrum of the adduct corresponds to thepresence of a large number of absorbing and emitting species. Indeed, alarge number of chromophores would account for the absence of any clearisosbestic points in the electronic spectra. The adduct is, in fact,fluorescent; the strong fluorescence prevented any detection of a Ramansignal at 752-nm laser excitation, despite repeated efforts.

Rh complexes are known to have charge-transfer transitions at higherenergies; however, interference from solvent DMSO lower than 300 nmmakes monitoring these transitions an unreliable task. The DMSO solutionof derivatized nanotubes can be readily diluted by organic solvents,such as methanol, DMF, chloroform, and toluene, without precipitatingthe tubes and with little change in the electronic spectrum of thediluted solutions. Similar optical behavior was reported forSWNT-aniline solutions. Upon dilution with acetone, however, a new peakat 330 nm is observed, which could be indicative of the presence ofcharge-transfer phenomenon in the adduct.

In general, the near-IR of dried, commercially available SWNTs in airshow three characteristic optical absorptions at 0.67, 1.3, and 1.9 eV(approximately at 5400; 10,000 and 16,000 cm⁻1, respectively), which canbe attributed to optical transitions between van Hove singularities ofthe density of electronic states of these tubes; the first twotransitions are assigned to semiconducting tubes, whereas the feature at1.9 eV can be attributed to the first pair of such singularities inmetallic tubes. The observed peaks are due to overlapping van Hovetransitions from all nanotube sizes that are present.

The presence of bands in the near-IR spectra of the functionalizednanotubes (FIG. 6) indicates that the electronic structure of the tubesis preserved, showing that the tubes are functionalized throughcoordinative attachment through dangling carboxyl and/or alcoholicgroups. This thus precludes coordination across electron-deficientdouble bonds. At the same time, the large number of transitions observedalso implies a broad-diameter distribution of tubes in the sample. TheNIR spectra presented are shown with the regions of strong solventabsorbance omitted. The spectrum from the functionalized adduct showssome clear differences from that of the raw nanotube sample.

Of particular significance is the presence of substructure andresolution of some of these peaks in the adduct spectrum, where onlybroad, unresolved humps had been seen for the raw, underivatizednanotubes. Because the width of the features in the NIR spectrumoriginates from the overlap of transitions from tubes of differentdiameters and helicities, the greater spectral resolution of peaksobserved shows that certain discrete diameter distributions of nanotubesare preferentially solubilized. In other words, there is a degree ofsize and diameter selectivity, associated with the derivatizationreaction and accompanying solubilization process.

Spectra for two different concentrations of the adduct are shown in FIG.6. It is clear that the peak positions are not significantly affected bydilution. The major bands observed correspond to S₁₁ and S₂₂, thetransitions between the first and second pairs of singularities for thesemiconducting tubes. The band at 5404 cm⁻¹, (0.67 eV) is consistentwith that of transitions observed for tubes with calculated diametersclose to 1.3 nm. Bands are also noted at 5968 and 6614 cm⁻¹ (0.74 and0.82 eV), which correspond to S₁₁ transitions of tubes of 1.2 and 0.84nm diameter, respectively. The corresponding S₂₂ transitions are locatedat 10565, 7178-7340, and around 8146 cm⁻¹ (1.31, 0.89-0.91, and around1.01 eV), respectively. The S₂₂ transitions in particular are shifted toslightly higher energy in the adduct and show greater resolution. Sincethe interband transition energy is inversely proportional to the tubediameter, these data are indicative of preferential derivatization anddissolution of smaller-diameter tubes. The other implication is that thefunctionalization reaction may have the effect of slightly narrowingdown the overall distribution of diameters in the sample, namely byskewing it toward smaller tubes, which would also lead to the higherspectral resolution observed. A doping-related upshift cannot be ruledout; however, charge transfer would be expected to have a greater effecton the S₁₁ transitions.

To demonstrate the presence of “metallicity” in the adducts,fluorescence data was obtained on these structures. In the presentsystems, the origin of luminescence is attributed to the existence ofextensive conjugated electronic structures and the excitation-energytrapping associated with defects in the nanotubes. The luminescencestudies (FIG. 7 a) in DMSO indicated that the emission spectrum isstrongly dependent on excitation wavelength, which is indicative of thepresence of a large number of emitters and absorbers. In fact, dependingon the excitation wavelength used, two distinct classes of emittingspecies can be differentiated. One class can be probed upon excitationover a wide number of wavelengths in the range from 315 to 720 nm,corresponding to the presence of solubilized nanotube moieties. Theemission spectra also contain a number of peaks of varying intensity inthe 600-750 nm region, which likely originate from the first emissionband of metallic SWNTs (M₁₁ transitions). The second class of emittersappears to be derived from the attached metal-containing complexes, morespecifically the Rh species, which emit strongly upon excitation ataround 350 nm. Emission spectra in this region show structure, which canbe attributed to a superposition of emission from excitable Rh speciesonto the broader, almost Gaussian nanotube emission spectra.

Functionalization facilitates the manifestation of the intrinsicluminescence, emanating from these tubes, through dispersion of thesenanotubes as well as trapping of the excitation energy on the nanotubesurface itself. The slow motion of the tubes in solution suggests thatthis energy is not lost rapidly, and thus, the observed quenching andcorresponding deactivation rate through molecular motion is slower.Furthermore, the emission spectrum upon excitation at 385 nm (FIG. 7 b)shows a red-shift of the emission maximum from 457 nm in theacetone-diluted solution to 483 nm for the MeOH-diluted solution. Suchan observed shift with increasing solvent polarity corroborates thepresence of charge separation in the excited state in theSWNT-Wilkinson's adduct.

Adduct Comprising Carbon Nanotube and Crown Ethers

Nanotube Purification and Bucky Paper Synthesis. Raw SWNTs (HiPco:average diameters of 0.7 to 1.1 nm) were purified by a mild nitric acidreflux followed by filtration using a polycarbonate membrane with a porediameter of 0.2 μm. This process generates surface functionalities,particularly carboxylic acids at nanotube ends and sidewall defectsites. The bucky paper mat thereby obtained was then redispersed in 12.1N HCl and briefly sonicated to remove the metal catalyst. Upon thesecond filtration, the precipitate was washed thoroughly with largeamounts of deionized water and placed in a vacuum oven at 180° C.

To create the derivatized adduct, the purified bucky paper was initiallyground up with a 3:1 mass excess of 2-aminomethyl-18-crown-6 ether(Aldrich) (CE), a clear yellow, viscous liquid, to form a black paste;CE readily moistened and permeated the bucky paper. Next, 1 mL ofdistilled deionized water was added. The mixture was swirled, sonicatedfor 1 s, and then allowed to stand for 1 h, after which an additional 9mL of distilled water was added followed by vigorous stirring. Theresultant mixture was filtered by a polycarbonate membrane to separateout unfunctionalized or partially functionalized SWNT precipitate,yielding a dark-brown solution, which could be further dried by heatingunder an Ar flow to form a black paste, the SWNT-CE adduct.

The paste could then be dissolved in many organic solvents such asmethanol, ethanol, 2-propanol, acetone, o-dichlorobenzene (ODCB),dimethylformamide (DMF), tetrahydrofuran (THF), dimethyl sulfoxide(DMSO), ethyl acetate, and benzene. Excess, unreacted CE could beremoved from the adduct by washing with diethyl ether. Prior tocharacterization, the solutions were passed through a column packed withglass wool to remove excess solid particulate matter in order to obtainan optically clear solution. The resultant solutions were visuallynonscattering and were appropriately diluted for optical measurements.

The optical characteristics of SWNTs in solution were monitored by theabsorbance at 500 nm; the derivatized crown ether does not absorb beyondthat value. Quantitative concentrations were calculated using opticalabsorption data fitted to a Beer-Lambert plot. Representative solubilityvalues are listed in Table 1.

Results Crown ethers containing an amino functionality attached to apendant methylene side chain on the macrocyclic ring were attached tothe nanotube. The amino group of 2-aminomethyl-18-crown-6 interacts withoxygenated groups, particularly the carboxylic acid sites, at the endsof the purified tubes as well as at oxidized defect sites scatteredalong the sidewalls. The crown ether's maerocyclic ring dangles from theSWNT. Evidence that it does comes from ¹H NMR data (FIG. 8). The protonson the macrocyclic ring contribute to a broad resonance in the 3.6 to3.8 ppm range, whereas the methylene side chain resonances appear in the2.6 ppm region, where a pair of quartets is evident. The macrocyclicproton resonances remain strong in the SWNT-CE adduct, whereas themethylene side chain resonances are widened to the point of almostdisappearing. This signal attenuation for protons in functionalizingmoieties in close physical proximity to SWNTs has been previouslyreported. Indeed, the observed broadening of these latter resonancesoccurs because of localization of the methylene side chains onto theSWNTs coupled with slow tumbling of the adduct in solution, preventingrotational averaging, as well as the presence of large diamagnetic ringcurrents in the tubes.

To further ascertain the conformational nature of SWNT-CE bonding withinthe adduct, the adduct was incubated with a solution of lithium chlorideto observe the Li cation movement; ⁷Li NMR was performed on the adductmixture in MeOH. In a solution of pure crown ether, because of the fastexchange kinetics between the Li⁺ complexed within the cavity of thecrown ether and the free, solvated cation, only one ⁷Li peak is visible.In a solution of the SWNT-CE adduct, a single narrow Li peak wasobserved, similarly implying the presence of fast exchange between Lications residing in the crown ether cavities within the SWNT-CE adductand those free in solution. Whereas exchange between CE and theoxygenated sites on the SWNTs may be possible, the fact that only one Lipeak was observed shows, supported by ¹H NMR, that the macrocyelic ringis tethered to the SWNT through an interaction involving the aminomethylside chain and that the ring freely dangles. Thus, the crown ether canreadily complex with the Li cation.

Optically, the presence of a sharp peak at 1105 cm⁻¹ in the mid-IR range(FIG. 9 a) for dried SWNT-CE adducts indicates C—O—C ether bondsoriginating from the crown ether; this band is slightly shifted from theether peaks observed in free CE. Fluorescence spectra (FIG. 9 b, c) showthat the functionalized adduct fluoresces strongly with an emissionmaximum at 455 nm. The excitation spectra shows that the fluorescingmoiety is the crown ether chromophore because the free unreacted crownether absorbs in the 360- to 370-nm region and fluoresces with anemission maximum near 408 nm. Indeed, the fact that the fluorescencesignal is not quenched but remains undiminished shows that themacrocyclic ring freely dangles from the tubes as opposed to wrappingdirectly around the SWNTs. The electronic structure of the chromophoreis unlikely to be strongly coupled with that of the SWNT itself, showingthat there is no disruption of the π conjugation within the nanotubeelectronic structure.

The emission peak is wider in the SWNT-CE adduct, an effect arising fromslower tumbling of the larger nanotubes in solution, which would therebyslow self-quenching of the fluorescence due to molecular motion. Theseresults further show the SWNT-CE adduct formation.

The SWNT-CE adduct arises from a zwitterionic interaction between aprotonated amine on CE and an oxyanion from a carboxylic acid group,creating a COO⁻NH₃ ⁺ ionic bond.

The exfoliation of nanotube ropes into individual tubes can beascertained by means of microscopy. Compared with the raw tubes, the AFMand TEM images (FIG. 11) of the adducts show several bundles of SWNTaggregates between diameters of ˜30 and ˜200 nm. The lengths of theseadduct bundles are shorter than those of the raw SWNT material, likelybecause of the etching effects of HNO₃.

The macrocycles may preferentially orient and alignrelative to eachother, projecting outward and parallel to the tubular axis, therebyfacilitating the formation of larger bundles. In addition, it has beenshown that oxidative derivatization can cause smaller tubes to associateinto larger bundles because of H-bonding between carboxyl groupsattached to the walls of functionalizing tubes, thereby adding to theoverall stacking effect.

Thus, while there have been described what are presently believed to bethe preferred embodiments of the present invention, other and furtherembodiments, modifications, and improvements will be known to thoseskilled in the art, and it is intended to include all such furtherembodiments, modifications, and improvements and come within the truescope of the claims as set forth below.

1. An adduct comprising a carbon nanotube and a transitional metalcoordination complex, wherein the metal of the complex is attached by acovalent linkage to at least one oxygen moiety on the nanotube.
 2. Anadduct as in claim 1 wherein said covalent linkage is a coordinativelinkage.
 3. An adduct as in claim 1 wherein said at least one oxygenmoiety is selected from the group consisting of a carboxyl group, ahydroxyl group, an aldehyde group and a ketone group.
 4. An adduct as inclaim 1 wherein the transitional metal coordination complex is selectedfrom the group consisting of Wilkinson's complex, [Ag(NH₃)₂]⁺,[Cu(NH₃)₄]²⁺, [Fe(CN)₆]⁴⁻, [Fe(CN)₆]³⁻, [Co(NH₃)₆]³⁺, [Pt(NH₃)₂Cl₂],[Cr(ethylenediamine)₃]³⁺, [Pt(NH₃)₄]²⁺, Fe(C₅H₅)₂, Ni(C₅H₅)₂, [PdCl₄]²⁻,Cr(CO)₆, [Ni(NH₃)₆]²⁺, [CoF₆]³⁻, [Pt(ethylenediamine)₂Cl₂]Br₂, [Co(NH₃)₄(SCN)Br]Cl, [Fe(H₂O)₆]³⁺, [CeCl₆]²⁻, [La(acetylacetone)₃ (H₂O)₂],[Nd(H₂O)₉]³⁺, [Er(NCS)₆], [Lu(2,6-dimethylphenyl)₄]⁻ and[Ho(tropolonate)₄]⁻.
 5. An adduct as in claim 1 wherein saidtransitional metal is in the form of a nitrate, a halide, or a salt. 6.An adduct as in claim 4 wherein said adduct comprises different types oftransitional metal coordination complexes.
 7. An adduct as in claim 1wherein said adduct has high degree of solubility in organic or aqueoussolvents.
 8. An adduct as in claim 7 wherein said organic solvent isselected from the group consisting of dimethylsulfoxide (DMSO),tetrahydrofuran (THF) or dimethylformamide (DMF). methanol, ethanol,2-propanol, acetone, o-dichlorobenzene (ODCB), dimethylsulfoxide (DMSO),tetrahydrofuran (THF), ethyl acetate, benzene and dimethylformamide(DMF).
 9. An adduct as in claim 4 wherein the transitional metalcoordination complex is a Wilkinson's complex.
 10. An adduct as in claim9 wherein said adduct is a hexacoordinate structure.
 11. An adduct as inclaim 9 wherein the rhodium of said Wilkinson's complex has an oxidationstate of three.
 12. An adduct as in claim 9 wherein said adduct has asolubility of greater than 250 mg/L in DMSO.
 13. An adduct as in claim 9wherein said adduct has a solubility of greater than 75 mg/L in THF orDMF.
 14. An adduct as in claim 1 wherein said carbon nanotube is asemi-conductor.
 15. An adduct as in claim 1 wherein said carbon nanotubeis a metal.
 16. An adduct as in claim 1 wherein said carbon nanotube issingle-walled.
 17. An adduct as in claim 1 wherein said carbon nanotubeis multi-walled.
 18. An adduct as in claim 16 wherein the diameter ofsaid single-walled carbon nanotube is about 0.7 to about 1.5 nm.
 19. Anadduct as in claim 14 wherein the diameter of said multi-walled carbonnanotube is about 3 to about 30 nm.
 20. An adduct as in claim 1 whereinat least one end of the carbon nanotube is open.
 21. A method ofproducing a plurality of carbon nanotubes with increased solubility, themethod comprising: adding a solution comprising a transitional metalcoordination complex to a carbon nanotube dispersion to form a resultantdispersion comprising carbon nanotube-metal adducts, wherein a pluralityof carbon nanotubes with increased solubility is formed.
 22. A method asin claim 21 wherein 50-99 wt % of said carbon nanotube-metal adductdispersion comprises nanotubes.
 23. A method as in claim 21 wherein saidtransitional metal coordination complex is selected from the groupconsisting of Wilkinson's complex, [Ag(NH₃)₂]⁺, [Cu(NH₃)₄]²⁺,[Fe(CN)₆]⁴⁻, [Fe(CN)₆]³⁻, [Co(NH₃)₆]³⁺, [Pt(NH₃)₂Cl₂],[Cr(ethylenediamine)₃]³⁺, [Pt(NH₃)₄]²⁺, Fe(C₅H₅)₂, Ni(C₅H₅)₂, [PdCl₄]²⁻,Cr(CO)₆, [Ni(NH₃)₆]²⁺, [CoF₆]³⁻, [Pt(ethylenediamine)₂Cl₂]Br₂, or[Co(NH₃)₄ (SCN)Br]Cl, [Fe(H₂O)₆]³⁺, [CeCl₆]²⁻, [La(acetylacetone)₃(H₂O)₂], [Nd(H₂O)₉]³⁺, [Er(NCS)₆], [Lu(2,6-dimethylphenyl)₄]⁻, and[Ho(tropolonate)₄]⁻.
 24. A method as in claim 23 wherein a transitionalmetal is in the form of a nitrate, a halide, or a salt.
 25. A method asin claim 23 wherein the solution comprises a mixture of differenttransitional metal coordination complexes.
 26. A method as in claim 21wherein the nanotube dispersion comprises nanotubes in DMSO, THF or DMF.27. A method as in claim 21 further comprising precipitating the adductfrom the solution.
 28. A method of catalyzing a reaction of anunsaturated hydrocarbon comprising: providing a catalyst systemcomprising a carbon nanotube-transitional metal coordination complexadduct in an organic solvent; and contacting a reactant and anunsaturated hydrocarbon with said catalyst system, whereby a reaction ofthe unsaturated hydrocarbon and the reactant is catalyzed.
 29. A methodas in claim 28 wherein said reaction is selected from the groupconsisting of a hydrogenation, a hydroformylation, an epoxidation, anolefin metathesis, a hydrosilylation, and an alkene (Ziegler-Natta)polymerization.
 30. A method as in claim 28 wherein said organic solventis a halogenated organic solvent.
 31. A method as in claim 30 whereinsaid halogenated organic solvent is CHCl₃.
 32. A method as in claim 28wherein said transitional metal coordination complex is selected fromthe group consisting of Wilkinson's complex, [Ag(NH₃)₂]⁺, [Cu(NH₃)₄]²⁺,[Fe(CN)₆]⁴⁻, [Fe(CN)₆]³⁻, [Co(NH₃)₆]³⁺, [Pt(NH₃)₂Cl₂],[Cr(ethylenediamine)₃]³⁺, [Pt(NH₃)₄]²⁺, Fe(C₅H₅)₂, Ni(C₅H₅)₂, [PdCl₄]²⁻,Cr(CO)₆, [Ni(NH₃)₆]²⁺, [CoF₆]³⁻, [Pt(ethylenediamine)₂Cl₂]Br₂, or[Co(NH₃)₄ (SCN)Br]Cl, [Fe(H₂O)₆]³⁺, [CeCl₆]²⁻, [La(acetylacetone)₃(H₂O)₂], [Nd(H₂O)₉]³⁺, [Er(NCS)₆], [Lu(2,6-dimethylphenyl)₄]⁻, and[Ho(tropolonate)₄]⁻.
 33. A method as in claim 32 wherein a transitionalmetal is in the from of a nitrate, a halide, or a salt.
 34. A method asin claim 28 wherein the hydrocarbon is an alkene, an acetylene, analkadiene, a cycloolefin, a cycloacetylene, a cycloalkene, an alkyne, acyclohexene or an aromatic compound.
 35. A method as in claim 28 furthercomprising recovering the adduct from the catalyst system.
 36. A methodas in claim 28 wherein said transitional metal complex is a Wilkinson'scomplex and wherein said reaction is a hydrogenation of an unsaturatedhydrocarbon.
 37. A catalyst support comprising a plurality of adductswherein an adduct comprises a carbon nanotube and a transitional metalcoordination complex, wherein the metal of the complex is associated bycoordinative attachment to at least one oxygen moiety on the nanotube,and wherein the transitional metal coordination complex is capable ofcatalyzing a reaction.
 38. A method of exfoliating a plurality of carbonnanotube bundles, comprising: contacting a carbon nanotube dispersioncomprising a plurality of nanotube bundles wherein the bundles have anaverage first diameter with a solution comprising transitional metalcoordination complexes, thereby exfoliating the bundles, wherein theexfoliated bundles have an average second diameter.
 39. A method as inclaim 38 wherein said average second diameter is about 10-80% of saidaverage first diameter.
 40. A method as in claim 38 wherein saidexfoliated bundles are about 15-20 nm in diameter.
 41. A method as inclaim 38 wherein said bundles are exfoliated to a single nanotube.
 42. Amethod of providing single carbon nanotubes and carbon nanotube bundleswith a selected diameter, comprising: contacting a carbon nanotubedispersion with a solution comprising a transitional metal coordinationcomplex, wherein adducts are formed between single nanotubes and saidtransitional metal complex, and between carbon nanotube bundles of aselected diameter and said transitional metal complex, wherein theselected diameter is less than about 10 nanometers; and precipitatingthe adducts from the solution, wherein carbon nanotubes with a selecteddiameter are provided.
 43. A method of modifying a physical property ofa nanotube wherein the method comprises: contacting a carbon nanotubewith a solution of a transitional metal coordination complex to form acarbon nanotube-transitional metal coordination complex adduct, whereina physical property of the carbon nanotube is modified.
 44. A methodaccording to claim 43 wherein the physical property is selected from thegroup consisting of an electronic property, an electrical property, anelectromechanical property, an optical property, a chemical property, amechanical property, a structural property, a thermal property and athermoelectric property.
 45. A method according to claim 44 wherein theelectrical property is selected from the group consisting ofconductance, resistivity, carrier mobility, a transport property,permittivity, and a charge transfer property.
 46. A method according toclaim 45 wherein the modification of conductance is a tunability inconductance.
 47. A method according to claim 44 wherein the structuralproperty is selected from the group consisting of elasticity and ease ofcomposite formation.
 48. A device comprising an adduct wherein theadduct comprises a carbon nanotube and a transitional metal coordinationcomplex, wherein the metal of the complex is associated by coordinativeattachment to at least one oxygen atom on the nanotube, wherein thedevice is selected from the group consisting of a sensor, a device usedin molecular electronics, a solar cell, a device used inoptoelectronics, a device used in nanocatalysis, and a scanning probemicroscopy tip.
 49. An adduct comprising a carbon nanotube and amacrocyclic molecule, wherein a functional group attaches themacrocyclic molecule and the nanotube.
 50. An adduct as in claim 49wherein said macrocyclic molecule is selected from the group consistingof a coronand, a corand, a cryptand, a spherand, a cryptaspherand, ahemisspherand, a podand, a cavitand, a carcerand, and derivativesthereof.
 51. An adduct as in claim 49 wherein the macrocyclic moleculecomprises oxygen, nitrogen or sulfur atoms.
 52. An adduct as in claim 50wherein the macrocyclic molecule forms a cavity which is about 0.5 to 10Angstroms.
 53. An adduct as in claim 50 wherein the macrocyclic moleculecomprises a metal ion is selected from the group consisting of a lithiumion, a potassium ion, a calcium ion, a mercury ion, a zinc ion, astrontium ion, and a magnesium ion.
 54. An adduct as in claim 49 whereinsaid macrocyclic molecule and said carbon nanotube are covalentlylinked.
 55. An adduct as in claim 49 wherein said macrocyclic moleculeand said carbon nanotube are ionically linked.
 56. An adduct as in claim49 further comprising an organic molecule linker between the functionalgroup and the macrocyclic molecule, wherein the linker comprises lessthan about twenty carbon atoms.
 57. An adduct of claim 49 wherein theadduct has high degree of solubility in an organic solvent or an aqueoussolvent.
 58. The adduct of claim 57 wherein the organic solvent isselected from the group consisting of methanol, ethanol, 2-propanol,acetone, o-dichlorobenzene (ODCB), dimethylsulfoxide (DMSO),tetrahydrofuran (THF), ethyl acetate, benzene and dimethylformamide(DMF).
 59. An adduct according to claim 50 wherein the macrocyclicmolecule is a crown ether.
 60. An adduct according to claim 59 whereinthe crown ether has a cavity size from about 1.7 to 3.0 Angstroms. 61.An adduct according to claim 59 wherein the ring of the crown ethercomprises approximately fifteen to forty-four atoms.
 62. An adductaccording to claim 61 wherein the crown ether is selected from the groupconsisting of 12-crown-4,15-crown-5,18-crown-6,27-crown-9, 30-crown-10,and dicyclohexano-18-crown-6.
 63. An adduct of claim 49 wherein thecarbon nanotube is a semi-conductor.
 64. An adduct of claim 49 whereinthe carbon nanotube is a metal.
 65. An adduct of claim 49 wherein thecarbon nanotube is single-walled.
 66. An adduct of claim 49 wherein thecarbon nanotube is multi-walled.
 67. An adduct of claim 65 wherein thediameter of the single-walled carbon nanotube is about 0.7 to about 1.5nmn.
 68. An adduct of claim 66 wherein the diameter of the multi-walledcarbon nanotube is about 3 to about 30 nm.
 69. A method of producing aplurality of carbon nanotubes with increased solubility, the methodcomprising: providing a plurality of carbon nanotubes in the form ofbucky paper; and dispersing the bucky paper in a solution comprising aplurality of macrocyclic molecules to form a resultant dispersioncomprising a plurality of nanotube-macrocyclic molecule adducts, whereina plurality of carbon nanotubes with increased solubility is produced.70. The method of claim 69 wherein said macrocyclic molecule is selectedfrom the group consisting of a coronand, a corand, a cryptand, aspherand, a cryptaspherand, a hemisspherand, a podand, a cavitand, acarcerand, and derivatives thereof.
 71. The method of claim 69 whereinthe nanotube has functional groups selected from the group consisting ofan amino group, a keto group, an aldehyde group, an ester group, anhydroxyl group, a carboxyl group, and a thiol group.
 72. The method ofclaim 69 wherein the macrocyclic molecule has functional groups selectedfrom the group consisting of an amino group, a keto group, an aldehydegroup, an ester group, an hydroxyl group, a carboxyl group, and a thiolgroup.
 73. The method of claim 69 wherein the macrocyclic moleculesolution comprises is a mixture of different macrocyclic molecules. 74.The method of claim 69 further comprising recovering the adducts fromthe resultant dispersion by filtration.
 75. The method of claim 69wherein the macrocylic molecule is a functionalized crown ether.
 76. Themethod of claim 32 wherein the crown ether is selected from the groupconsisting of 12-crown-4,15-crown-5,18-crown-6,27-crown-9,30-crown-10,and dicyclohexano-18-crown-6 and mixtures thereof.
 77. A method ofexfoliating a plurality of carbon nanotube bundles, comprising:contacting bucky paper with a solution comprising functionalizedmacrocyclic molecules, wherein said bucky paper comprises a plurality ofnanotube bundles having an average first diameter, thereby exfoliatingthe bundles, wherein the exfoliated bundles have an average seconddiameter.
 78. The method of claim 77 wherein the average second diameteris about 10-80% of the average first diameter.
 79. The method of claim35 wherein the exfoliated bundles are about 30 to 200 nm in diameter.80. A method of modifying a physical property of a nanotube wherein themethod comprises: providing a plurality carbon nanotubes in the form ofbucky paper; and dispersing the bucky paper in a functionalized crownether solution to form a resultant dispersion comprising nanotube-crownether adducts, wherein a physical property of the carbon nanotube ismodified.
 81. A method according to claim 80 wherein the physicalproperty is selected from the group consisting of an electronicproperty, an electrical property, an electromechanical property, anoptical property, a chemical property, a mechanical property, astructural property, a thermal property and a thermoelectric property.82. A method according to claim 80 wherein the electrical property isselected from the group consisting of conductance, resistivity, carriermobility, a transport property, permittivity, and a charge transferproperty.
 83. A method according to claim 82 wherein the modification ofconductance is a tunability in conductance.
 84. A method according toclaim 81 wherein the structural property is selected from the groupconsisting of elasticity and ease of composite formation.
 85. A devicecomprising an adduct wherein the adduct comprising a carbon nanotube anda functionalized crown ether, wherein a functional group on the crownether is attached to an oxygen atom on the nanotube, wherein the deviceis selected from the group consisting of a sensor, a device used inmolecular electronics, a solar cell, a device used in optoelectronics, adevice used in nanocatalysis, and a scanning probe microscopy tip.